Role of Phytochromes in Shade AvoidanceEcophysiological and Molecular aspects

Shade avoidance syndrome

Plants adapt to changes in light conditions

-Shade Avoidance Syndrome-

R/FR =

photon fluence rate in 10 nmband centered on 660 nm

photon fluence rate in 10 nmband centered on 730 nm

Photoreceptors in Arabidopsis

Phytochromes A-E

Phytochrome signal transduction

Phytochrome structure and chromophore-Reception-

chromophorephytochromobilin

PHY apoprotein

PHY holoprotein

125 kDa monomer

Native phytochrome occurs as a dimer of 2 equivalent subunits

Phytochrome function in Arabidopsis-Response-

Phytochrome signal transduction

Phytochrome signal transduction-emerging themes-

I. Subcellular partitioningPhytochrome nucleocytoplasmic trafficking

good correlation between the wavelength requirement for physiologicalresponses and nuclear import of the different phytochromes

phyA

minutes

phyB

hours

I. Subcellular partitioningPhytochrome nucleocytoplasmic trafficking

II. Proteolytic degradationPhytochrome

phyA

The ubiquitin/26S proteasome pathwaymajor proteolytic pathway in plants and animals

The ubiquitin/26S proteasome pathway

Light signal transduction-mutant analysis: light vs dark-

Long Hypocotyl 5 - HY5

long hypocotyl in R, FR and B

Phytochrome signal transduction-cop/det/fus mutants-

COP/DET/FUSname

Other proteinname Function

Putative ubiquitin ligase component

COP9 signalosome subunit

COP9 signalosome subunit

COP9 signalosome subunit

COP9 signalosome subunit

COP9 signalosome subunit

COP9 signalosome subunit

E2 Ub-conjugating enzymevariant

Not cloned

Protein required for HY5 degrad.

COP1

DET1

COP10

COP16

COP11

FUS12

FUS11

COP8

FUS5

COP9

CSN1

CSN2

CSN3

CSN4

CSN7

CSN8

Phytochrome signal transduction-cop/det/fus mutants-

F

Phytochrome signal transduction- cop/det/fus mutants -

COP1 - HY5 interaction

Phytochromes (PHY) –responses to red and far-red light-

Phytochrome signal transduction-more sophisticated screens: light quality-

Mutants that exhibit light-grown characteristics in the dark

Mutants that exhibit altered seedling development under specific light conditions

e.g. Far-red light (phyA)

Wt phyA phyAspa1 Wt rsf1

Phytochrome signal transduction-identified mutants-

Phytochrome signal transduction-proteolytic degradation-

Phytochrome signal transduction-phytochrome interacting factors-

Yeast two-hybrid analysis

Isolation of Phytochrome Interacting Factor3-a basic helix-loop-helix transcription factor protein-

PIF3 negatively regulates phyB- but not phyA- mediated inhibition of hypocotyl elongation

Phytochrome signal transduction-bHLH class PIF3-like transcription factors-

III. Phosphorylation-Phytochromes are similar to histidine kinases-

Two component signaling-intermezzo-

III. Phosphorylation -Phytochrome Ser/Thr-kinase activity-

III. Phosphorylation-phytochrome phosphorylation status; PAPP5-

III. Phosphorylation-Phytochrome Ser/Thr-kinase activity; external targets-

Phytochrome signal transduction-phosphorylation of phytochrome interacting factors-

IV. Regulation of transcription

phytochrome responses are associated with massive alterations in gene expression

44% (far-red light) and 25% (red light) of early light-responsive genes (< 1 hr) encode transcription factors

IV. Regulation of transcription-Immediate phytochrome targets-

IV. Regulation of transcription-light/phytochrome responsive promoters-

Light regulated transcription factors-transcription-

Light regulated transcription factors-post-transcriptional regulation; phosphorylation-

Light regulated transcription factorspost-transcriptional regulation;

phosphorylation, cellular localization

Light regulated transcription factors-post-transcriptional regulation; degradation-

PIF3 as an examplecellular trafficking, gene expression, phosphorylation, degradation

Phytochrome signalingFurther downstream targets; phytohormones